ABSTRACT Collecting ground-based images of environmental scenes usually results in images with significant depth of field and strongly oblique views of the objects of interest. These factors complicate quantitative analysis by introducing large changes in scale within images and, in the case of thermal data, varying the corrections required to account for atmospheric attenuation. We report on the use of photogrammetric and machine vision techniques to combine spatial data with thermal imagery in order to allow distance, velocity and appropriately corrected thermal data to be obtained. Topographic information was determined by photogrammetry, using visible images from a consumer-grade digital SLR camera which were collected simultaneously with the thermal images. Orientation of the thermal images (i.e. calculation of camera position and pointing direction) then allowed viewing distance corrections to be applied to the thermal images on a pixel-by-pixel basis. Rectification of the corrected images allows them to be presented in geographic coordinates and therefore facilitates correlation with other datasets for analysis. Examples are given from the 2004 to 2005 eruption of Mount Etna, Sicily. Images were collected from flow front regions just south of Monte Centenari, approximately 2 km from the active vent. From the viewing positions occupied, the lava flowed towards the camera, with distances to the flow being between ~50 and 400 m. We describe the viewing distance corrections applied to the thermal data and illustrate how sequence analysis in a 3D spatial context can be used to determine flow profiles and lava flux rates. Significant variations in flux can be correlated with periods of levee building, breaching and ogive formation.
